Wastewater is often co-contaminated with chromium, chelating agents, and chloride. Influences of Cr(3+) speciation on Cr phytoremediation by Ipomonea aquatica were investigated. MINEQL+ was employed to estimate Cr speciation. Statistic regression was used to investigate the relationships between Cr speciation and accumulation. I. aquatica accumulated high Cr concentration (13,217 mg kg(-1)) in the root at Cr(3+) of 10 mg l(-1) and EDTA of 10(-4) M after 14 d growth. Pearson correlation analysis indicates that root Cr concentration significantly correlated with Cr-EDTA speciation (r = 0.67, p < 0.05) and Cr-Cl speciation (r = 0.91, p < 0.01). Shoot Cr concentration also significantly correlated with Cr-Cl speciation (r = 0.97, p < 0.01). An increase in Cl(-) concentration to 1.72 x 10(-4) M enhanced root Cr concentration; however, the accumulation of root Cr was in hibited at high Cl(-) concentration (5.76 x 10(-5) M). Microscopic image showed that a high portion of Cr(3+) accumulated on the root surface. (C) 2009 Elsevier Ltd. All rights reserved.